This invention relates to the art of making heat-treated polybenzoxazole fibers.
It is known to spin and heat-treat fibers that contain polybenzazole polymer. See, e.g., Wolfe, U.S. Pat. No. 4,533,693 (Aug. 5, 1985) at col. 166-174; Takeda, Japanese Kokai 2(1990)-84511 (published Mar. 26, 1990): and Ledbetter et al., "An Integrated Laboratory Process for Preparing Rigid Rod Fibers from the Monomers," The Materials Science and Engineering of Rigid Rod Polymers at 253, 259-61 (Materials Research Society 1989), which are incorporated herein by reference. Ordinarily, a dope is formed containing the polymer and a solvent acid. The dope is forced through a spinnerette and drawn across an air gap. It is contacted with a coagulating liquid, usually water, to coagulate the polymer and form a fiber. The fiber is washed to remove residual acid. The resulting fiber is heat-treated to improve its modulus.
Within those broad process steps there is still significant room for improvement. The most desirable process conditions may vary from fiber to fiber. What is needed is a process specifically adapted for making the best polybenzoxazole fibers.